1. Field of the Invention
The present invention relates to an image pickup apparatus or an image processing apparatus such as a digital camera.
2. Related Background Art
Recent advancement of video apparatuses such as digital cameras is remarkable. Not only are they used merely as cameras, but also demands for using them as image input apparatuses of computers are strong and rapidly prevailing.
FIG. 1 is a block diagram showing the structure of a conventional single-plane digital camera. An object image (not shown) is focused via a lens 1 and an optical low-pass filter 14 onto a focal plane of an image pickup element 2.
A shutter release button for instructing image pickup is structured to be depressed by two steps. As a user half-depresses the shutter release button, the camera enters a pre-photographing state in which AE (auto-exposure), AF (auto-focussing) and the like are performed to determine an opening of an iris, a shutter speed, a focal position, and the like. As the user fully depresses it to the second step, the camera enters a real photographing state.
In the real photographing state, an object image entering the image pickup element 2 is photoelectrically converted into an image signal which is output to the next stage.
The image signal output from the image pickup element 2 is digitalized by an A/D converter 3 and supplied to a signal processing unit 10 whereat an image compression process such as JPEG is performed and thereafter the processed image signal is stored in a recording device.
In a single-plane type, color filters having layouts such as shown in FIG. 2 are disposed in front of the image pickup element in order to form color signals.
In FIG. 2, the left side shows a pixel layout of complementary color filters (Ma: magenta, Cy: cyan, Ye: yellow, G: green) and the right side shows a pixel layout of saturated color filters (R: red, G: green, B: blue).
Generally, according to the Nyquist theorem, an object image having a spatial frequency higher than half the sampling frequency N generates a low frequency signal in the form of aliasing distortions.
To avoid this, a low-pass filter (called an optical low-pass filter) for cutting frequencies higher than N/2 is disposed on the image pickup plane of an image pickup element, in order to mainly prevent color moire to be caused by color filters.
It is however obvious that using such a low-pass filter lowers a resolution, so that there is a demerit that an image of a high quality corresponding to the number of pixels of an image pickup element cannot be formed.
It is an object of the present invention to solve the above problems and provide an image pickup apparatus and an image processing apparatus capable of taking an image of a high quality without any defects such as color moire.
It is another object of the present invention to provide an image pickup apparatus having a simple structure capable of forming a color image of a high quality.
In order to achieve the above objects, a preferred embodiment of the present invention discloses an image pickup apparatus comprising: image pickup means for picking up an image and outputting an image pickup signal; control means for performing a first photographing in an in-focus state to obtain a first image pickup signal and performing a second photographing in a state defocused by a predetermined amount from the in-focus state to obtain a second image pickup signal; and signal processing means for generating a luminance signal in accordance with the first image pickup signal, and chrominance signals in accordance with the second image pickup signal.
It is another object of the present invention to provide an image pickup apparatus and an image processing apparatus capable of forming an image of high grade quality without fluctuation of luminance, color and resolution.
In order to achieve the above object, a preferred embodiment of the present invention discloses an image pickup apparatus comprising: means for inputting a first image pickup signal and a second image pickup signal both picked up in a relative state defocused by a predetermined amount; luminance signal generating means for generating a luminance signal from the first image pickup signal; chrominance signal generating means for generating chrominance signals from the second image pickup signal; and control mens for performing an iris priority photographing by fixing an iris while the first and second image pickup signals are picked up.
Another preferred embodiment of the invention discloses an image processing apparatus comprising: means for inputting a first image pickup signal and a second image pickup signal both picked up in a relative state defocused by a predetermined amount; luminance signal generating means for generating a luminance signal from the first image pickup signal; luminance step removing mens for removing a step of a level of the luminance signal; chrominance signal generating means for generating chrominance signals from the second image pickup signal; position difference correcting mens for correcting a relative position difference between the luminance signal with the removed luminance step and the other color difference signals; and output means for outputting the luminance and chrominance signals with the position difference being corrected by the position difference correcting means.